We propose to investigate visual transduction in isolated retinas from humans and the monkey Macaca fascicularis. The overall aims are twofold: a) to elucidate the laws that govern the conversion of light to neural signals, and b) to clarify the molecular mechanism of this conversion. By making electrical recordings from single photoreceptor cells we will approach the following questions: 1. How do human rods respond t light and adapt in backgrounds? What are their spectral sensitivities? 2. What are the spectral sensitivities and response properties of human blue cones? 3. What are the kinetics of changes in intracellular Ca++ concentration in primate photoreceptors, and how do these changes regulate transduction? 4. What is the rate of spontaneous activation of primate cone pigments in darkness? 5. By what mechanisms do the proteins of the "red" and "green" cone pigments regulate light absorption in the 11-cis retinal chromophore? 6. What are the photosensitivities of the three cone pigments? 7. What is the organization of the cone inputs within the receptive fields of ganglion cells in the primate retina? Information on these points will improve our understanding of human vision and its disturbances in disease.